1. Field of the Invention
The present invention relates to an improvement in an alternator control system to control a terminal voltage of a vehicle battery.
2. Description of Related Art
In an alternator control system, described, for instance, in Japanese Unexamined Patent Publication No. 60-106338, for controlling an alternator, the voltage of a vehicle battery, charged by the alternator, is feedback controlled so as to maintain an established or required voltage. In the process of the battery voltage feed-back control, a terminal voltage of the vehicle battery is compared against the established or required voltage, and if the battery voltage falls below the required voltage, a transistor is activated at a proper duty rate so as to provide a field current to the alternator's three-phase field coil to replenish the battery's charge. Conversely, if the battery voltage becomes above the required voltage, the transistor is de-activated to allow the vehicle battery to discharge.
When exercising the feedback control of field current according to the deviation between the battery voltage and the required voltage so as to closely align the battery voltage with the required voltage, although a field current is applied to the field coil to produce a generated current, proportional to the field current, through the armature coil, even if applying an accurate field current, its actual wave form becomes deformed or distorted due to great interference of inductance of the field coil. Conventionally, as shown in FIG. 11, in the event that a field current changes, even though a required field current is established as depicted by a solid line, an actual field current causes a delay of change, as depicted by a dotted broken line, which is followed by a corresponding delay of change in generated current of the armature coil. This results in a drop in actual voltage of the vehicle battery, as depicted by a solid line, from a required voltage depicted by a broken line. This leads to an accompanying decline in control performance when the alternator changes its load and/or its speed of rotation.